This invention relates to engine combustion chamber and valve train arrangements and, more particularly, to a valve train arrangement for a twin cam three-valve engine.
It is known in the engine art to provide engine combustion chambers with one or more intake valves and one or more exhaust valves, each arrangement having various advantages and disadvantages. Dual valve arrangements are generally provided for engines where simplicity or economy of manufacture is preferred. Three or four valve arrangements are often provided where the intention is to provide higher horse power output for the same size engine cylinder displacement. Four valve engines are commonly provided with dual overhead camshafts.
U.S. Pat. No. 5,560,329 issued Oct. 1, 1996 to the assignee of the present invention provides a two-valve combustion chamber arrangement in a V-type engine having dual in-block camshafts, one of which actuates the intake valves of the engine and the other of which actuates the exhaust valves. Both camshafts are driven by the engine crankshaft. A cam phasing device is provided for varying the phase angle of one of the camshafts with respect to the other camshaft and the crankshaft. This arrangement allows variable valve timing of the intake or exhaust valves in order to provide improved engine performance at varying speeds and loads. A push rod actuated valve train allows cam phasing with a single cam phaser acting on one of the camshafts as opposed to multiple cam phasers required for accomplishing the same purpose in a dual overhead camshaft engine with multiple cylinder banks.
The present invention provides a valve train somewhat similar to that disclosed in the previously-mentioned patent combined with a three-valve combustion chamber arrangement. The combustion chamber has a pair of side-by-side intake valves on an intake side of a cylinder and a single exhaust valve on an opposite exhaust side of the combustion chamber or cylinder. The dual camshaft arrangement in a V-type or multi-bank engine provides the same advantages that the arrangement does in the above-noted patent. However, the use of dual intake valves with a single exhaust valve provides much improved intake port airflow for improved specific output compared to a single intake valve engine, while the retention of a single exhaust valve provides better catalytic converter performance due to lower exhaust heat loss than in four-valve engines of the same output capability. Use of a single exhaust valve also provides for better placement of a direct cylinder injector with improved injector targeting over other overhead valve and four-valve engine designs for improved emissions and fuel economy.
The simplified valve train still provides the capability of hydraulic lash adjustment for each valve in the layout and the two camshaft drive provides the advantages of cam phasing for one or both camshafts with one or two cam phasers, respectively. The single exhaust valve may be conventionally actuated by a pushrod to one side of the cylinder, allowing a coplanar arrangement of the exhaust valve and pushrod with a rocker arm acting in the same plane and the valve head placed flush with the combustion chamber surface surrounding the valve seat.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.